This invention relates in general to universal joints, and in particular to an apparatus for supplying and retaining a lubricant within various rotating parts of universal joints.
Universal joints are well known devices which provide a driving connection between two members adapted to rotate about non-aligned axes of rotation. Universal joints are widely used between rotatable drive shaft sections in vehicle drive train systems. A typical universal joint includes a cross having a central body portion with four cylindrical trunnions extending outwardly from the cross. The trunnions are oriented in a single plane and extend at right angles relative to one another, and the trunnions have a common intersection at the center of the central body portion.
A hollow cylindrical bearing cup is mounted on the end of each of the trunnions. Needle beatings or similar means are provided between the outer cylindrical surfaces of the trunnions and the inner cylindrical surfaces of the bearing cups to permit relative rotational movement between the trunnions and the beating cups. The bearing cups which are mounted on an opposed pair of the trunnions can be connected to a first end yoke secured to an end of a first drive shaft section, while the bearing cups mounted on a second opposed pair of the trunnions can be connected to a second end yoke secured to an end of a second drive shaft section.
The bearings between the bearing cups and the trunnions require lubrication. Universal joint trunnions often are hollowed out with central bores adapted for supplying a lubricant to the beatings. The central bores of each of the four trunnions can be joined, at their common intersection, with a lubrication bore or conduit which supplies lubricant to the four central bores from a single fitting. Under this arrangement, each of the central bores is in direct communication with each other. This facilitates the lubrication process. Upon rotation of the universal joint, the centrifugal force of rotation ensures that a sufficient quantity of lubricant flows along the trunnion central bores toward the bearings. When the universal joint is not rotating, such as when the vehicle is at rest, the centrifugal force is not present, and the lubricant can flow by gravity from the central bore of an upwardly oriented trunnion down into the central bores of the other trunnions. This problem generally occurs during warm weather, when the lubricant is apt to flow more readily. When the vehicle is then started, the universal joint will temporarily be without lubricant at the one affected bearing, until the centrifugal force of rotation can replenish the supply of lubricant to the bearing. Operating the universal joint without adequate lubricant, even for a short time, causes undue wear on the mechanism.
It is known to position check valves inside the central bores of the trunnions to prevent the lubricant from flowing backward (away from the bearings) when the universal joint is not rotating. The use of check valves in each of the central bores is generally satisfactory for maintaining lubricant in the bearings. However, positioning check valves within the central bores of the trunnions complicates the insertion of lubricant into the trunnion central bores. Ideally, the central bores would be filled with lubricant, or prelubricated, before shipping to the location where the universal joint is assembled. When check valves are used in each of the trunnion central bores, however, the lubricant can be deposited within the central bores only after the check valves are in place. This precludes prelubrication prior to shipping. Accordingly, it would be desirable to provide a lubrication system for a universal joint where there are no check valves in the trunnion central bores so that they can be lubricated prior to shipping. Also, it is desirable for such a lubrication system to be able to prevent the drainback of lubricant while the universal joint is not rotating.